docs(material/datepicker): require confirmation buttons for a11y (#24526)
docs(material/datepicker): require confirmation buttons for a11y (#24526)

For the datepicker accessiblity documentation, add instructions to always
provide confirmation buttons. This prevents an accessibility issue where
selecting a date on the calendar gives no audio feedback of the selected date
(#23568).

This commit only affects the docs and does not change source code.

Addresses #23568
crisbeto/material2,crisbeto/material2,crisbeto/material2,angular/components,crisbeto/material2,angular/components,angular/components,angular/components